1. Field of the Invention
This invention relates to a hydraulic change speed system for a working vehicle having a gear type change speed device shiftable by an actuator, a hydraulic clutch connected to a power transmission line including the gear type change speed device, a valve unit for switching operative states of the hydraulic clutch, and a controller for controlling the valve unit. In this hydraulic change speed system, the controller depressurizes the hydraulic clutch to begin disengaging the hydraulic clutch in response to a start of operation of the actuator, and pressurizes the hydraulic clutch to start engaging the hydraulic clutch in response to a finish of operation of the actuator. The operation of the valve unit is interlocked to the operation of the actuator. The hydraulic clutch is pressurized rapidly from for a set time from start of an operation to engage the hydraulic clutch, and pressurized gradually after the set time.
2. Description of the Related Art
In the hydraulic change speed system for a working vehicle noted above, the valve unit switches the hydraulic clutch in response to an operation of the actuator for shifting the gear type change speed device. This eliminates the trouble of manually operating the clutch to break power transmission temporarily during a gear shifting operation. Further, for the set time from the start of an operation to engage the hydraulic clutch, the controller increases the speed of pressuring the hydraulic clutch by the valve unit. A reduced time is required for engaging the hydraulic clutch, compared with the case of gradually pressuring the hydraulic clutch by the valve unit. After the set time, the controller controls the valve unit to pressurize the hydraulic clutch gradually, thereby suppress a shock occurring with a clutch engagement.
In such a mechanism for a working vehicle, an engaging operation of the hydraulic clutch is started upon completion of a gear shifting operation from neutral position when the vehicle is started. At this time, pressure oil is supplied to the hydraulic clutch completely empty of pressure oil. On the other hand, when an engaging operation of the hydraulic clutch is started upon completion of a gear shifting operation while the vehicle is running, pressure oil is supplied to the hydraulic clutch not completely empty of pressure oil. Thus, different quantities of pressure oil are required, after a shifting operation in time of starting the vehicle and after a shifting operation during a run, at an initial stage of an operation to engage the hydraulic clutch and immediately before a clutch engagement while reducing time consumed in engaging the hydraulic clutch.
Conventionally, the above set time is extended for a gear shifting operation performed when starting the vehicle, and shortened for a gear shifting operation performed during a run. After a shifting operation performed when starting the vehicle and after a shifting operation performed during a run, different quantities of pressure oil (pressurizing characteristics) are obtained during the set time at an initial stage of the operation to engage the hydraulic clutch from start of the clutch engaging operation. Depending on whether the shifting operation is performed when starting the vehicle or during a run, the time required after the shifting operation to engage the hydraulic clutch is appropriately shortened, while suppressing a shock occurring with a clutch engagement.
However, the quantity of pressure oil drained from the hydraulic clutch during a shifting operation carried out by operating the actuator is variable with the duration of the shifting operation and viscosity of the pressure oil. The quantity of pressure oil supplied to the hydraulic clutch per unit time after the shifting operation is variable with the viscosity and flow rate of the pressure oil. In the prior art noted above, only the set time is varied for a shifting operation performed when starting the vehicle and a shifting operation performed during a run. It is impossible to carry out an appropriate operation to engage the hydraulic clutch by taking the duration of the shifting operation and the viscosity and flow rate of pressure oil into account.
An object of this invention is to provide a hydraulic change speed system for a working vehicle having an excellent shifting performance with a hydraulic clutch engageable appropriately after a gear shifting operation, which is achieved by taking the duration of the shifting operation and the viscosity and flow rate of pressure oil into account, and considering various factors overlooked in conventional hydraulic change speed systems.
Another object of this invention is to reduce a dead time from completion of a shifting operation with a finish of actuator operation to a clutch engagement.
The above objects are fulfilled, according to this invention, by a hydraulic change speed system as noted in the outset hereof, comprising a time measuring device for measuring a shifting time of the gear type change speed device, wherein, based on the shifting time measured, the controller sets a predetermined time for pressurizing the hydraulic clutch rapidly from a start of engagement of the hydraulic clutch.
The longer time the shifting operation by the actuator takes, the longer time is consumed in the disengaging operation of the hydraulic clutch by the depressurizing action of the valve unit started with a start of operation of the actuator. This increases the quantity of pressure oil drained from the hydraulic clutch. A correspondingly increased quantity of pressure oil is needed to operate the hydraulic clutch appropriately until immediately before a clutch engagement during an initial stage of an operation to engage the hydraulic clutch. The system according to this invention takes this fact into account. The longer the time taken in the shifting operation is as measured by the time measuring device, the longer time is set by the controller for opening the valve unit. Thus, an increased quantity of pressure oil is obtained during the predetermined time. The quantity of clutch operating pressure oil increased with the length of time of the shifting operation is attained promptly for appropriately operating the hydraulic clutch until immediately before a clutch engagement. This effectively avoids a dead time produced by the opening degree of the valve unit restricted from a stage considerably before a clutch engagement to pressurize the hydraulic clutch gradually, which would occur where the predetermined time is fixed despite an extended time for shifting the gear type change speed device by the actuator.
Conversely, the shorter time the shifting operation by the actuator takes, the shorter time is consumed in the disengaging operation of the hydraulic clutch by the depressurizing action of the valve unit started with a start of operation of the actuator. This decreases the quantity of pressure oil drained from the hydraulic clutch. A correspondingly decreased quantity of pressure oil is needed to operate the hydraulic clutch appropriately until immediately before a clutch engagement during an initial stage of an operation to engage the hydraulic clutch. The shorter the time taken in the shifting operation is as measured by the time measuring device, the shorter time is set by the controller for opening the valve unit. Thus, a decreased quantity of pressure oil is obtained during the predetermined time. The quantity of clutch operating pressure oil decreased with the length of time of the shifting operation is attained promptly for appropriately operating the hydraulic clutch until immediately before a clutch engagement. This effectively avoids a shock produced by engagement of the hydraulic clutch occurring during the predetermined time where the predetermined time is fixed despite a shortened time for shifting the gear type change speed device by the actuator.
That is, in engaging the hydraulic clutch after a shifting operation of the gear type change speed device by the actuator, a varied quantity of pressure oil may be needed at an initial stage of the clutch engaging operation to operate the hydraulic clutch appropriately until immediately before a clutch engagement. However, with reference to the time taken in the shifting operation, the predetermined time for increasing the opening degree of the valve unit is set to a length for obtaining a necessary quantity of pressure oil at that time. As a result, regardless of variations in the shifting time, a shock is suppressed in time of a clutch engagement with increased effect while shortening the time required for engaging the hydraulic clutch appropriately.
Thus, the hydraulic change speed system for a working vehicle according to this invention has an excellent change speed performance, which takes lengths of time of shifting operations into account. After a shifting operation of the gear type change speed device by the actuator, the time required for engaging the hydraulic clutch is shortened appropriately, and a shock is suppressed in time of a clutch engagement with increased effect.
The foregoing objects are fulfilled, according to this invention, by a hydraulic change speed system as noted in the outset hereof, comprising an oil temperature measuring device for detecting a temperature of pressure oil in the hydraulic change speed system, the controller setting the predetermined time based on the temperature detected.
In a shifting operation performed when starting the tractor, in which the hydraulic clutch is only engaged by supplying pressure oil to the hydraulic clutch completely empty of pressure oil, when the temperature of pressure oil lowers to increase its viscosity, the pressure oil flows less easily and a less quantity of pressure oil is supplied to the hydraulic clutch per unit time. As a result, an extended time is required to obtain the quantity of pressure oil for appropriately operating the hydraulic clutch (and thus the pressure applied to the hydraulic clutch) until immediately before a clutch engagement. The system according to this invention takes this fact into account. The lower the temperature of pressure oil is as detected by the oil temperature measuring device, the longer time is set by the controller for opening the valve unit. Thus, the quantity of pressure oil (the pressure applied to the hydraulic clutch) is attained promptly for appropriately operating the hydraulic clutch until immediately before a clutch engagement. This effectively avoids a dead time produced by the opening degree of the valve unit restricted from a stage considerably before a clutch engagement to pressurize the hydraulic clutch gradually, which would occur where the predetermined time is fixed despite a high viscosity of pressure oil.
Conversely, when the temperature of pressure oil rises to decrease its viscosity, the pressure oil flows easily and an increased quantity of pressure oil is supplied to the hydraulic clutch per unit time. As a result, a reduced time is required to obtain the quantity of pressure oil for appropriately operating the hydraulic clutch (the pressure applied to the hydraulic clutch) until immediately before a clutch engagement. The higher the temperature of pressure oil is as detected by the oil temperature measuring device, the shorter time is set by the controller for opening the valve unit. Thus, the quantity of pressure oil (the pressure applied to the hydraulic clutch) is attained properly for appropriately operating the hydraulic clutch until immediately before a clutch engagement. This effectively avoids a shock produced by engagement of the hydraulic clutch occurring during the predetermined time where the predetermined time is fixed despite a low viscosity of pressure oil.
On the other hand, in a shifting operation performed during a run, which involves an operation to disengage the hydraulic clutch by draining pressure oil therefrom and an operation to engage the hydraulic clutch by supplying pressure oil thereto, the lower the temperature of pressure oil is, the less quantity of pressure oil drained from the hydraulic clutch per unit time and the less quantity of pressure oil is supplied to the hydraulic clutch per unit time. A quick operation is required in disengaging the hydraulic clutch, and thus the valve unit is opened to a large degree. When the hydraulic clutch is engaged, the valve unit is once adjusted to a small degree in order to prevent a shock occurring in time of clutch engagement. As a result, the viscosity of pressure oil affects its fluidity more in time of an engaging operation than in time of a disengaging operation. The lower the temperature of pressure oil is to result in the higher viscosity, the greater is the difference between the quantity of pressure oil drained from the hydraulic clutch per unit time during an operation to disengage the hydraulic clutch and the quantity of pressure oil supplied to the hydraulic clutch per unit time during an operation to engage the hydraulic clutch. An increased quantity of pressure oil is required for appropriately operating the hydraulic clutch until immediately before a clutch engagement. When the oil temperature measuring device detects a low temperature of pressure oil, the controller extends the predetermined time for increasing the opening degree of the valve unit to obtain an increased quantity of pressure oil during the predetermined time. In this way, the quantity of pressure oil is increased according to the difference between the quantity of pressure oil drained from the hydraulic clutch per unit time and the quantity of pressure oil supplied to the hydraulic clutch per unit time. The increased quantity of pressure oil is attained promptly for appropriately operating the hydraulic clutch until immediately before a clutch engagement. This effectively avoids a dead time produced by the opening degree of the valve unit restricted from a stage considerably before a clutch engagement to pressurize the hydraulic clutch gradually, which would occur where the predetermined time is fixed despite a high viscosity of pressure oil.
The higher the temperature of pressure oil is to result in the lower viscosity, the smaller is the difference between the quantity of pressure oil drained from the hydraulic clutch per unit time during an operation to disengage the hydraulic clutch and the quantity of pressure oil supplied to the hydraulic clutch per unit time during an operation to engage the hydraulic clutch. A decreased quantity of pressure oil is required for appropriately operating the hydraulic clutch until immediately before a clutch engagement. When the oil temperature measuring device detects a high temperature of pressure oil, the controller shortens the predetermined time for decreasing the opening degree of the valve unit to obtain a decreased quantity of pressure oil during the predetermined time. In this way, the quantity of pressure oil is decreased according to the difference between the quantity of pressure oil drained from the hydraulic clutch per unit time and the quantity of pressure oil supplied to the hydraulic clutch per unit time. The decreased quantity of pressure oil (i.e. pressure applied to the hydraulic clutch) is attained properly for appropriately operating the hydraulic clutch until immediately before a clutch engagement. This effectively avoids a shock produced by engagement of the hydraulic clutch occurring during the predetermined time where the predetermined time is fixed despite a low viscosity of pressure oil.
That is, in engaging the hydraulic clutch after a shifting operation of the gear type change speed device by the actuator, a varied quantity of pressure oil (i.e. clutch pressure) may be needed at an initial stage of the clutch engaging operation to operate the hydraulic clutch appropriately until immediately before a clutch engagement, or a varied time may be needed to obtain that quantity of pressure oil (i.e. clutch pressure). However, with reference to the viscosity of pressure oil determined from the temperature thereof, the predetermined time for increasing the opening degree of the valve unit is set to a length for obtaining a necessary quantity of pressure oil at that time. As a result, regardless of variations in the viscosity of pressure oil, a shock is suppressed in time of a clutch engagement with increased effect while shortening the time required for engaging the hydraulic clutch appropriately.
Thus, the hydraulic change speed system for a working vehicle according to this invention has an excellent change speed performance, which takes the viscosity of pressure oil into account. After a shifting operation of the gear type change speed device by the actuator, the time required for engaging the hydraulic clutch is shortened appropriately, and a shock is suppressed in time of a clutch engagement with increased effect.
The foregoing objects are fulfilled, according to this invention, by a hydraulic change speed system as noted in the outset hereof, comprising a speed measuring device for detecting a speed of an engine that drives a hydraulic pump to produce a hydraulic pressure for the hydraulic change speed system, the controller setting the predetermined time based on the speed detected.
The lower the engine speed is, the hydraulic pump delivers pressure oil at the lower flow rate. An extended time is required to obtain the quantity of pressure oil at an initial stage of an operation to engage the hydraulic clutch, for appropriately operating the hydraulic clutch until immediately before a clutch engagement. The system according to this invention takes this fact into account. The lower the engine speed is as detected by the speed measuring device, the longer time is set by the controller for opening the valve unit. Thus, the quantity of pressure oil is attained promptly for appropriately operating the hydraulic clutch until immediately before a clutch engagement. This effectively avoids a dead time produced by the opening degree of the valve unit restricted from a stage considerably before a clutch engagement to pressurize the hydraulic clutch gradually, which would occur where the predetermined time is fixed despite a low flow rate of pressure oil.
Conversely, when the engine speed increases, the hydraulic pump delivers pressure oil at an increased flow rate. As a result, a reduced time is required to obtain the quantity of pressure oil for appropriately operating the hydraulic clutch until immediately before a clutch engagement. The higher the engine speed is as detected by the speed measuring device, the shorter time is set by the controller for opening the valve unit. Thus, the quantity of pressure oil (the pressure applied to the hydraulic clutch) is attained properly for appropriately operating the hydraulic clutch until immediately before a clutch engagement. This effectively avoids a shock produced by engagement of the hydraulic clutch occurring during the predetermined time where the predetermined time is fixed despite an increased flow rate of pressure oil.
That is, in engaging the hydraulic clutch after a shifting operation of the gear type change speed device by the actuator, a varied quantity of pressure oil may be needed at an initial stage of the clutch engaging operation to operate the hydraulic clutch appropriately until immediately before a clutch engagement. However, with reference to the engine speed, the predetermined time for increasing the opening degree of the valve unit is set to a length for obtaining a necessary quantity of pressure oil at that time. As a result, regardless of variations in the quantity of pressure oil supplied from the hydraulic pump, a shock is suppressed in time of a clutch engagement with increased effect while shortening the time required for engaging the hydraulic clutch appropriately.
This invention proposes a system having at least two features selected from three features consisting of a feature of the controller setting the predetermined time based on the shifting time measured, the controller setting the predetermined time based on the temperature detected, and the controller setting the predetermined time based on the engine speed detected. This system suppresses a shock in time of a clutch engagement with increased effect while shortening the time required for engaging the hydraulic clutch appropriately.
Further, this invention proposes a system in which, immediately after the predetermined time, the controller once reduces a valve controlling current value for the valve unit below a valve controlling current value for adjusting the valve unit to realize a target pressurizing characteristic for obtaining an appropriate engaging pressure for the hydraulic clutch.
In this system, the valve controlling current value for the valve unit is reduced below the valve controlling current value for adjusting the valve unit, immediately after the predetermined time, to realize a target pressurizing characteristic for obtaining an appropriate engaging pressure for the hydraulic clutch. A correspondingly increased operating force is applied to throttle the valve unit immediately after the predetermined time. A sufficient force is thereby secured to act against the spool of the valve unit sticking to a valve wall due to the viscosity of oil during the predetermined time for operating the valve unit with a rapid pressurizing characteristic. Consequently, the valve unit may be throttled promptly immediately after the predetermined time.
As a result, the operation to throttle the valve unit is carried out, immediately after the predetermined time, without a delay caused by the spool of the valve unit sticking to the valve wall due to the viscosity of oil. This avoids an inconvenience that the hydraulic clutch is engaged to generate a shock at a stage where a large quantity of pressure oil is supplied to the hydraulic clutch in the course of throttling the valve unit from a large opening degree to the target opening degree. A shock is prevented from occurring in time of clutch engagement due to the spool sticking to the valve wall.
With the suppression of a delay in the operation to throttle the valve unit due to the spool sticking to the valve wall, the predetermined time need not be extended for operating the valve unit work (i.e. increasing the opening degree of the valve unit) with the rapid pressuring characteristic. The time required for engaging the hydraulic clutch does not become long.
Thus, a shock is suppressed in time of clutch engagement due to the spool sticking to the valve wall while shorting the time required for engaging the hydraulic clutch.
Further, as a preferred embodiment, immediately after the predetermined time, the controller may once reduce the valve controlling current value for the valve unit to zero. Then, a maximum operating force is applied to throttle the valve unit immediately after the predetermined time. A sufficient force is thereby secured to act against the spool sticking to the valve wall due to the viscosity of oil. Consequently, the valve unit may be throttled promptly immediately after the predetermined time.
Further, the foregoing objects are fulfilled, according to this invention, by a hydraulic change speed system as noted in the outset hereof, in which the valve unit includes a selector valve for switching pressure oil supply lines to the hydraulic clutch, and an electromagnetic proportional valve for adjusting pressurizing characteristics for the hydraulic clutch, the electromagnetic proportional valve being connected in series to and upstream of the selector valve on an oil line extending from the hydraulic pump to the hydraulic clutch, the controller causing the electromagnetic proportional valve to start pressurizing the hydraulic clutch before a finish of operation of the actuator.
In the system according to this invention, the controller opens the electromagnetic proportional valve before a finish of operation of the actuator. Thus, when the selector valve is switched to a pressure oil supplying position to engage the hydraulic clutch in response to an end of operation of the actuator, the hydraulic clutch is immediately supplied with pressure oil at a high flow rate corresponding to the electromagnetic proportional valve operating with a rapid pressure characteristic. That is, the quantity of pressure oil to be supplied to the hydraulic clutch is not limited while the electromagnetic proportional valve is opened, which is the case when the electromagnetic proportional valve is opened after switching the selector valve to the pressure oil supplying position. A correspondingly reduced dead time occurs from completion of a shifting operation when the operation of the actuator ends to the clutch engagement. A reduction in vehicle speed in time of a shifting operation may be suppressed, effectively to suppress a shock occurring in time of a clutch engagement.
In a preferred embodiment, this system further comprises a speed discriminating device for determining a speed provided by the change speed device, wherein the controller is operable, based on a result of discrimination by the speed discriminating device, to vary a target pressurizing characteristic with which the electromagnetic proportional valve pressurizes the hydraulic clutch before the finish of operation of the actuator.
A certain speed stage may require a different shifting time. Then, a different quantity of pressure oil is drained from the hydraulic clutch during the shifting operation. As a result, a different quantity of pressure oil is needed for engaging the hydraulic clutch. Taking this aspect into account, the larger the quantity of pressure oil is drained from the hydraulic clutch during the shifting operation, the controller sets the more rapid target pressurizing characteristic for the electromagnetic proportional valve before an end of operation of the actuator, to increase the quantity of pressure oil supplied to the hydraulic clutch per unit time. Thus, regardless of speed stages, a sufficient quantity of pressure oil is secured during the predetermined time for appropriately operating the hydraulic clutch until immediately before a clutch engagement. This effectively avoids an inconvenience that, depending on a speed stage, the hydraulic clutch cannot be operated promptly during the predetermined time until immediately before a clutch engagement, resulting in an extended dead time from completion of a shifting operation when the operation of the actuator ends to a clutch engagement.
As a further preferred embodiment of the invention, the system may further comprise an oil temperature measuring device for detecting a engine speed in the hydraulic change speed system, wherein the controller is operable, based on the temperature detected by the oil temperature measuring device, to vary a target pressurizing characteristic with which the electromagnetic proportional valve pressurizes the hydraulic clutch before the finish of operation of the actuator. Then, the system has an excellent change speed performance, capable of reducing the dead time from completion of a shifting operation when the operation of the actuator ends to a clutch engagement, regardless of the temperature of pressure oil.
The system may further comprising a speed measuring device for detecting a speed of an engine that drives the hydraulic pump, wherein the controller is operable, based on the speed detected by the speed measuring device, to vary a target pressurizing characteristic with which the electromagnetic proportional valve pressurizes the hydraulic clutch before the finish of operation of the actuator. Then, the system has an excellent change speed performance, capable of reducing the dead time from completion of a shifting operation when the operation of the actuator ends to a clutch engagement, regardless of engine speed.
In a further preferred embodiment of the invention, the system further comprises a state discriminating device for determining whether the working vehicle is being started or already running, wherein the controller is operable, based on a result of discrimination by the state discriminating device, to vary a target pressurizing characteristic with which the electromagnetic proportional valve pressurizes the hydraulic clutch before the finish of operation of the actuator.
In a shifting operation performed during a run, pressure oil is supplied to the hydraulic clutch not completely empty of pressure oil. In a shifting operation performed when starting the vehicle, pressure oil is supplied to the hydraulic clutch completely empty of pressure oil. Taking this aspect into account, when starting the vehicle, the controller controls the electromagnetic proportional valve with a more rapid target pressurizing characteristic than when the vehicle is running, to increase the quantity of pressure oil supplied to the hydraulic clutch per unit time. Thus, whether the vehicle is being started or is already running, the hydraulic clutch is operated reliably during the predetermined time until immediately before a clutch engagement. This effectively avoids an inconvenience occurring in time or starting the vehicle, in which the hydraulic clutch cannot be operated properly during the predetermined time until immediately before a clutch engagement, and the opening degree of the electromagnetic proportional valve restricted from a stage considerably before the clutch engagement, resulting in an extended dead time from completion of a shifting operation when the operation of the actuator ends to the clutch engagement.
Other features and advantages of this invention will be apparent from the following description of the embodiments to be taken with reference to the drawings.